The disclosure of Japanese Patent Application No. 2000-271303 filed on Sep. 7, 2001, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a welding structure for a resin component which allows reliable attachment of the component to a fuel tank and also inhibits leakage of fuel, or the like, within the fuel tank.
2. Description of Related Art
There is great demand for improvement in the air tightness of fuel tank systems for fuel tanks, and in particular, for fuel tanks of automobiles, in order to suppress emissions of hydrocarbon gases into the surrounding environment, at times of both running and stopping. In order to improve the sealing of the entire fuel tank system in this manner, a key problem which must be solved is reducing the amount of hydrocarbon gases that leaks from the fuel tank itself, as well as from each component part attached directly or indirectly to the fuel tank, or in other words, from the points, and so forth, to which, for example, a connecting pipe, a valve member, a pump or a filter are attached.
Furthermore, in order to bring about both weight reduction and cost reduction of automobiles, plasticization of fuel tanks has been promoted. At present, fuel tanks made from a high-density polyethylene resin that offers good corrosion prevention and is light weight have become mainstream. Moreover, in line with this, endeavors have also been made to plasticize each component attached directly and indirectly to the fuel tank. As a result, in order to make attachment to the fuel tank easy, the same resin material has been utilized in the attachment portion of each component and the fuel tank, and a method for connecting them using thermal welding has been adopted.
In light of these circumstances, the components described hereinafter are commonly used for fuel tanks and resin components attached to fuel tanks.
In order to achieve fuel tank weight reduction, the fuel tank is integrally molded by blow molding with resin. High density polyethylene resin (HDPE) is utilized since it is suitable for blow molding and offers excellent affordability and shock resistance. However, this high density polyethylene resin is known to permeate small amounts of hydrocarbon gases. Even though this permeation is limited, some sort of countermeasure to address it is desirable in order to respond to rising concerns regarding recent environmental pollution issues. The laminated structure of the fuel tank wall shown in FIG. 12 has been proposed as a countermeasure.
In the figure, a fuel tank a is composed from a five layer structure that fundamentally includes a three layer structure having an inner shell b forming an inside portion of the tank, an outer shell c forming an outer portion of the tank, and a barrier layer d interposed between the shells b and c which prevents permeation of hydrocarbon gases. Bonding layers e, e are sandwiched between the barrier layer d and both of the shells b and c, respectively, in order to facilitate even stronger bonding of the respective resins.
More particularly, the inner shell b and the outer shell c use known high density polyethylene resin, and the bonding layers e, e use a highly advanced modified high density polyethylene resin having adhesive properties (this resin has adhesive properties and permeates hydrocarbon gases). The barrier layer d adopts a resin that prevents permeation by hydrocarbon gases, such as EVOH resin (EVAL) made by Kuraray Co., Ltd. Hydrocarbon gas emissions are suppressed very well using fuel tanks of this type.
A valve, intended as a part to be attached to a fuel tank, which is light and can be attached to the fuel tank and which reduces leakage of fuel, is disclosed in Japanese Patent Laid-Open Publication No. 10-71861. This valve is shown in FIG. 13. This invention relates to a fuel leakage prevention valve for preventing leakage of fuel from a fuel tank, which occurs when an automobile turns over, or such like.
In this invention, a resin part p includes a valve cylinder portion q and an attachment portion r, these members being formed, respectively, from different materials. The valve cylinder portion q is formed from a polyacetal resin possessing great rigidity and capable of being formed with high dimensional accuracy, and includes a disk portion h which is integrally insert molded with an attachment portion r, and a valve cylinder g housing a fuel leakage prevention valve f. The attachment portion r is formed from the same high density polyethylene resin material as the fuel tank a, and has a flange j formed in an abutting portion which abuts against the fuel tank a. Furthermore, a pipe portion k connecting with a connection pipe m is formed on an opposite side of the attachment portion r to the flange j. In addition, a resin component p is composed from the valve cylinder portion q and the attachment portion r which are integrally formed by placing the disk portion h of the valve cylinder portion q in the die, and insert molding the attachment portion. The integrally formed valve cylinder portion q and the attachment portion r are strongly fixed by thermal welding an upper surface of the fuel tank a and a lower surface of the flange j of the attachment portion r, when the valve cylinder g is inserted in an open portion i of the fuel tank a.
However, as a result of the valve cylinder portion q and the attachment portion r being formed from different resins, even if both the valve cylinder portion q and the attachment portion r are integrally molded, there is a chance that a gap will emerge between the valve cylinder portion q and the attachment portion r due to vibrations caused by use, contractions due to temperature variation, deterioration with time, or the like, during usage after molding. In theory, the valve should function so as to prevent leakage of fuel from the tank, when the car turns over, or the like. However, if a gap is generated, fuel may leak at such times.
As well as this, since the attachment portion r is formed from the same high density polyethylene resin material as the fuel tank a, hydrocarbon gases can permeate through the attachment portion and are released to the outside.
Moreover, in Japanese Patent Laid-open No. HEI. 6-270701 a resin component, namely, a connection pipe, is disclosed. This connection pipe, as shown in FIG. 14, is formed from a first member s made from a polyamide resin, and a second member t made from a modified high density polyethylene resin. As a result of forming the second member t from the modified high density polyethylene resin, a flexible pipe is provided, and as well as this, attachment to the fuel tank can be executed with greater ease. Furthermore, since the second member t possesses cohesive properties, connection with the connecting portion w of the first member s is improved.
However, according to this structure, the second member t is formed from high density polyethylene resin. As a result, hydrocarbon gases permeate through the second member t and are released to the outside.
It is an object of the invention to provide a welding structure for a resin component which inhibits leakage of fuel and hydrocarbon gases from the resin component connected to a fuel tank.
In order to achieve the above object, a welding structure according to a first aspect of the invention is structured such that, a fuel tank having a resin inner shell and a resin outer shell which are interposed by a fuel permeation prevention layer so as to be laminated, is welded to a resin component for attachment to the fuel tank. The resin component includes a body formed of a resin having low permeability to hydrocarbon gases, a packing material having low permeability to hydrocarbon gases which is fixed to the body, and a resin which is insert molded to at least a connecting portion of the body which connects with a connecting portion of the tank, and which is weldable to the fuel tank.
According to the first aspect, the fuel tank and the resin component are firmly fixed. Furthermore, leakage of fuel and permeation of hydrocarbon gases is reduced.
According to the first aspect, the packing material may be fixed by locking rings formed from the same resin as the insert molded resin. If such a structure is adopted, the seal of the layer interface of the body of the resin component and the insert molded resin is improved. As a result, for example, even if the interface connection of the elements to the upstream side of the packing material is inadequate (for example, the interface of the flange and the resin), or there is separation due to deterioration over time, and thus fuel leakage may potentially occur, fuel is reliably inhibited from leaking to the downstream side of the packing material because of the location of the packing material.
Moreover, a plurality of packing materials may be provided, thus making it possible to prohibit leakage of fuel with even greater reliability.
In addition, according to the first aspect, a concave and recess portion may be provided on a surface of the connecting portion side of the body that connects with the fuel tank, and the packing material may be provided in the recess portion. If such a structure is adopted, it is possible to inhibit leakage of fuel with even greater reliability due to the combined effect of the packing material and the concave and recess portion.
In a welding structure according to a second aspect of the invention, a fuel tank having a resin inner shell and a resin outer shell which are interposed by a fuel permeation prevention layer such that they are laminated, is welded to a resin component for attachment to the fuel tank. The resin component includes a body formed of a resin having low permeability to hydrocarbon gases, a protruding portion formed in a surface of a connecting portion side of the body that connects with the fuel tank and which penetrates into the outer shell of the fuel tank during attachment to the fuel tank, and a resin which is insert molded to at least a connecting portion of the body that connects with a connecting portion of the tank, and which is moldable to the fuel tank.
According to the second aspect, the fuel tank and the resin component are firmly fixed. Furthermore, leakage of fuel and permeation of hydrocarbon gases is reduced, and the size of a connecting surface between the fuel tank and the resin component is reduced. As a result, weigh reduction is achieved and production costs are reduced.
Furthermore, according to the second aspect, the protruding portion may penetrate into a bonding layer laminated on the upper surface of the fuel permeation prevention layer. In addition, if this structure is adopted, the protruding portion bonds with a bonding layer, thus preventing separation of the layer interfaces at this location. As a result, permeation of hydrocarbon gases is reduced and furthermore, leakage of fuel is reliably inhibited.
Moreover, according to the second aspect, the protruding portions may be inserted as far as the fuel permeation prevention layer. If this structure is adopted, the protruding portions extend as far as a barrier layer, and thus both fuel leakage due to layer interface separation, and permeation of hydrocarbon gases are inhibited.
Furthermore, the second aspect may include the packing material having low permeability to hydrocarbon gases which is fixed to the body. Accordingly, permeation of hydrocarbon gases is reduced, the area of the connecting surface of the fuel tank and the resin component is reduced, and as a result it is possible to reduce production costs and achieve weight reduction.
According to the second aspect, the packing material may be fixed by locking rings formed from the same resin as the insert molded resin. If this packing material is adopted, the seal of the interface between the body of the component and the insert molded resin is improved. As a result, even if the interface connection of the elements to the upstream side of the packing material is inadequate (for example, the interface of the flange and the resin), or there is separation due to deterioration over time, and thus fuel leakage may potentially occur, fuel is reliably inhibited from leaking to the downstream side of the packing material. Furthermore, it is also possible to inhibit permeation of hydrocarbon gases.